it's master bombmaker built the underwear bomb which nearly blew up an airliner over detroit on christmas day 2009. explosives hidden in printer cartridges and shipped on cargo planes bound for the u.s. were hard to detect, even after authorities had been told where to look. most recount, he designed a new underwear bomb which was handed over to the u.s. by a double agent. at a conference last month, john pistol, head of the transportation security administration, explained why it was so alarming. >> so it was a new type of explosive that we had never seen in either attempts in the u.s. or around the world by terrorists, so all of our explosive detection equipment which screens over a million checked bags every day-- just in the u.s.-- wasn't calibrated to detect that. >> reporter: but u.s. officials say they have no evidence the current plot is designed to take down airliners bound for the u.s. the embassy closings begin on sunday and could last for a number of days, depending on what more is learned about the threat. the travel alert will remain in effect through the end of august. >> s